The coverage area of selective call radio communication systems has been growing steadily, to the point where there are now nationwide systems in service and worldwide systems are in development. As these selective call radio communication systems grow, a need to uniquely identify all selective call radios that are authorized to operate on a particular selective call radio communication system has resulted in the assignment of longer identification numbers, or addresses, to the selective call radios, as well as the provision for the longer identification numbers within the signaling protocols used in the systems to communicate with the selective call radios.
In addition to providing for longer identification numbers, paging protocols for selective call radio communication systems, which have typically provided only outbound (from system to selective call radio) communication in narrowband (12.5 to 50 KHz) radio channels, have recently evolved to where some protocols provide high speed (greater than 4800 bits per second) outbound information transfer using a synchronous outbound protocol. The use of a synchronous outbound protocol improves the throughput by reducing the amount of air time used for bit and word synchronization of the receiver to the transmitted signal, and also improves battery savings in the selective call radios. Examples of high speed synchronous outbound protocols are the FLEX.TM. and ERMES (European Radio Message System) protocols, which provide for identification numbers having lengths of, respectively, 42 and 35 bits to assure uniqueness of all selective call radio units. Another evolutionary advancement in paging systems is the introduction of two way systems which provide for acknowledgment of an outbound message on an inbound channel, and may also provide for information other than acknowledgments to be communicated on the inbound channel. An example of a protocol for two way paging is ReFLEX.TM., which is based on the FLEX.TM. protocol for the outbound channel protocol.
In two way data radio communication systems, throughput is a primary design concern for both outbound and inbound information communication. Improved throughput allows more efficient use of limited radio spectrum and, generally, reduced latency (delay of delivery of the information). Another primary design concern in two way data radio communication systems is reduced power consumption of portable selective call radios. The use of lengthy identification numbers in both the outbound and inbound channels of a two way radio communication system increases the message lengths of the messages in both the inbound and outbound channels. In the inbound channel, the affect of increased message lengths on throughput is typically more severe than the affect in the outbound channel because of the random nature of contending inbound messages. In order to avoid loss of inbound messages which contend with each other, the inbound messages in many systems are organized by the system. Typical techniques for organizing inbound channel information include random access channel contention techniques, such as the ALOHA contention techniques and variations thereof (e.g., slotted ALOHA), well known to one of ordinary skill in the art, and scheduled responses, in which inbound information messages are scheduled by a system controller using outbound messages. These techniques amplify the negative affect of long identification numbers on throughput compared to the affect on outbound messages because, on the average, more than one message is sent for each inbound message to achieve the organization needed, and all the inbound messages must be identified. Reduced throughput of inbound messages, particularly by increasing the number of inbound messages, also reduces the average battery life of selective call radios used for generating inbound information, such as acknowledgment or status information.
Thus, what is needed is a technique for improving inbound throughput and the battery life of selective call radios in a two way radio communication system having a synchronous outbound protocol.